Phox2 and dHAND transcription factors select shared and unique target genes in the noradrenergic cell type.

The noradrenergic cell type is characterized by the expression of proteins involved in the biosynthesis, transport, and secretion of noradrenaline and is dependent on the sequential and combinatorial expression of numerous transcription factors, including Phox2a, Phox2b, dHAND, GATA2, GATA3, and MASH1. Phox2a and Phox2b transactivate the promoter of the gene encoding the noradrenergic biosynthetic enzyme, dopamine beta-hydroxylase (DBH), and dHAND potentiates the activity of Phox2a. In this study, we use chromatin immunoprecipitation assays to identify target genes of the Phox2 proteins and dHAND. All three proteins are bound to the DBH and PHOX2B promoter regions in SH-SY5Y neuroblastoma cells. The interaction between Phox2a and dHAND is analyzed by fluorescent anisotropy, which demonstrates that dHAND causes an eightfold increase in the affinity of Phox2a for its recognition sites on the DBH promoter region. The Phox2 proteins are not found on the genes encoding other noradrenergic enzymatic or transport proteins but are reciprocally bound to each other's promoters in SH-SY5Y cells. Together with Phox2a and Phox2b, dHAND is bound to the PHOX2B promoter and is also associated with the GATA2 and eHAND genes in the absence of the Phox2 proteins. These results demonstrate the direct interactions of the Phox2 and dHAND transcription factors within a noradrenergic cell type. The Phox2 proteins were found to share all target genes, whereas dHAND binds to genes independently of Phox2a.